In my post Prion, Garth! I had talked about mutant or misfolded SOD1 (mSOD1) spreading like a prion and infecting neighboring cells. A recently released study from Johns Hopkins shows for the first time in vivo that astrocytes expressing mutant mSOD1 damage the motor neurons they are supposed to protect. In the study, the authors transplanted SOD1G93A glial-restricted precursor cells—glial progenitors capable of differentiating into astrocytes—into the cervical spinal cord of rats to reveal how mutant astrocytes influence WT motor neurons and other cells types (microglia and astrocytes) in an in vivo setting. The G93A mutation of SOD1 is the most studied version of that particular genetic mutation responsible for many inherited (or familial) ALS cases.
This is the strongest evidence to date that “assaultrocytes” are primary culprits in ALS. It also further suggests that even some sporadic ALS can be caused by misfolded SOD1 which escapes proteasomal degradation and gets into the extracellular space. It also suggests that targeting mSOD1 and stem cell implantation of astrocytes can be viable treatment methods.
EDIT: Here is a more in-depth article by Amber Dance at the ALZ Forum.